Suture anchor with improved drive head

ABSTRACT

A suture anchor is provided including an elongate shank defining a longitudinal axis and having at least one bone-engaging thread formed thereon, and a drive head having a proximal end and a distal end mated to the elongate shank. The drive head has a substantially oval shape and includes at least one suture attachment member formed in a portion of the drive head. The configuration of the drive head is particularly advantages in that it provides a suture anchor having improved physical properties, including a high failure torque and a high stripping strength.

FIELD OF THE INVENTION

[0001] The present invention relates to suture anchors having improvedphysical properties, and in particular to suture anchors having a highfailure torque.

BACKGROUND OF THE INVENTION

[0002] Suture anchors are often used to attach a length of suture tobone in order to use the suture to secure detached soft tissue to thebone. Suture anchors typically have an anchor body, a suture attachmentfeature, and a bone engaging feature for retaining the suture anchorwithin bone. The anchor can be inserted into a preformed hole in thebone, and/or the anchor can be self-tapping and thus can include threadsfor mating the anchor within bone. Most suture anchors require the useof an insertion tool for driving the suture anchor into bone. Suchinsertion tools are typically formed from an elongate shank having amating feature formed on a distal end thereof for mating with acorresponding mating feature formed on or in the head of a sutureanchor. One common type of driver tool includes a hex-shaped orsquare-shaped socket for receiving a corresponding hex-shaped orsquare-shaped head of a suture anchor.

[0003] While conventional suture anchors and suture anchor drivers aresufficient, they have some drawbacks. Hex-shaped and square-shapedanchor heads, for example, tend to have a relatively low strippingstrength. This can be due to the structural integrity of the anchorhead, which is sometimes weakened by the attachment feature used toattach a suture to the anchor head. If the attachment feature decreasesthe amount of material on the anchor head that interfaces with thedriver, then the amount of material that needs to be removed or“stripped” from the drive head is reduced, thus reducing the strippingstrength of the head.

[0004] Conventional suture anchor heads also tend to have a relativelylow failure torque, which can result in shearing of the head duringinsertion. This type of failure can also be caused by the location ofthe suture attachment feature on the anchor head, which can reduce theoverall cross-sectional area of the drive head. The Bio-corkscrew™anchor, manufactured by Arthrex Inc., of Naples, Fla., is one example ofa suture anchor having a suture attachment feature that can interferewith the structural integrity of the anchor. In particular, a loop ismolded into and embedded within the anchor such that the loop extendsoutward from the head of the anchor to receive a suture. As a result ofthe placement of the looped suture through the anchor, the entire anchorhead is relatively weak and thus has the potential to shear off duringinsertion.

[0005] One option to increase the failure torque of an anchor head is toincrease the size of the head. Large anchor heads, however, require alarge driver tool, which in turn requires a relatively large bone tunnelto be formed in the bone. This is particularly undesirable, especiallywhere the bone tunnel is to be formed in the cancellous bone.Accordingly, most suture anchors are adapted to for use with arelatively small driver tool, and thus they have a relatively smalldrive head which can result in a low failure torque and a low strippingstrength.

[0006] Accordingly, there remains a need for suture anchors havingimproved physical properties, and in particular having a high failuretorque and a high stripping strength.

SUMMARY OF THE INVENTION

[0007] The present invention generally provides a suture anchorincluding an elongate shank defining a longitudinal axis and having atleast one bone-engaging thread formed thereon, and a drive head having aproximal end and a distal end mated to the elongate shank. The drivehead has a substantially oval shape and at least one suture attachmentmember formed in a portion of the drive head. The configuration of thedrive head is particularly advantageous in that it provides a sutureanchor having improved physical properties, including a high failuretorque and a high stripping strength. In an exemplary embodiment, thedrive head has a failure torque of at least about 5.0 inch pounds, andthe drive head has a tensile strength of at least about 60 pounds force(lbf).

[0008] In one embodiment, the suture attachment member comprises atleast one suture tunnel extending through the drive head, eithersubstantially transversely or such that the suture tunnel(s) intersectsthe longitudinal axis of the suture anchor. The suture attachment membercan also include a longitudinally oriented suture-receiving channelformed on an outer surface of the drive head and originating at andextending proximally from each opening of the at least one suturetunnel. In an exemplary embodiment, the suture tunnel(s) are formedproximal to the distal end of the drive head to present a channel-freeportion in the drive head. The channel-free portion provides additionalstructural integrity to the drive head of the suture anchor to minimizethe risk of shearing during insertion. In another exemplary embodiment,the drive head includes a first suture tunnel having a first pair ofopposed suture-receiving channels extending proximally therefrom, and asecond suture tunnel having a second pair of opposed suture-receivingchannels extending proximally therefrom.

[0009] In other aspects, a suture anchor and installation kit isprovided including at least one suture anchor and a cylindrical drivertool. The suture anchor has a shank with bone-engaging threads formedthereon and defining a longitudinal axis. A drive head is formed on theshank and has an oval shape with at least one longitudinally orientedsuture-receiving channel formed therein. The cylindrical driver tool hasa distal end with a socket formed therein having an oval shape adaptedto receive and engage the drive head of the suture anchor. In anexemplary embodiment, the driver tool has an outer diameter that isequal to or less than an outer-most diameter of the suture anchor.

[0010] Methods for using a suture anchor in accordance with the presentinvention are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will be more fully understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0012]FIG. 1A is a perspective view of a suture anchor according to oneembodiment of the present invention;

[0013]FIG. 1B is another perspective view of the suture anchor shown inFIG. 1A;

[0014]FIG. 1C is an enlarged, perspective view of the drive head portionof the suture anchor shown in FIG. 1A;

[0015]FIG. 1D is top view of the suture anchor shown in FIG. 1A;

[0016]FIG. 2A is a side view of one embodiment of the driver tool inaccordance with the present invention;

[0017]FIG. 2B is an end view of the distal-most end of the driver toolshown in FIG. 2A;

[0018]FIG. 3A is a top view illustration of the drive head of a sutureanchor in accordance with the present invention compared to two priorart suture anchor drive heads;

[0019]FIG. 3B is a top view illustration of the suture anchor driveheads shown in FIG. 3A having shaded areas illustrating the portion ofthe drive head that needs to be removed in order to strip the drivehead;

[0020]FIG. 4 is a chart illustrating the pullout tensile strength ofseveral different suture anchors compared to a suture anchor inaccordance with the present invention; and

[0021]FIG. 5 is a chart illustrating the failure torque of severaldifferent suture anchors compared to a suture anchor in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] As shown in FIGS. 1A and 1B, the present invention generallyprovides a suture anchor 10 including an elongate shank 12 defining alongitudinal axis A and having at least one bone-engaging thread 14formed thereon, and a drive head 16 having a proximal end 16 a and adistal end 16 b mated to the elongate shank 12. The drive head 16 has asubstantially oval shape and includes at least one suture attachmentmember formed therein. The configuration of the drive head 16 isparticularly advantages in that it provides a suture anchor 10 havingimproved physical properties, including a high failure torque and a highstripping strength.

[0023] The elongate shank 12 of the suture anchor 10 can have a varietyof configurations, and can include a variety of different bone-engagingfeatures formed thereon. FIGS. 1A and 1B illustrate an exemplaryembodiment of a bone anchor 10 having a shank 12 including a core 20with a single helical thread 14 extending around the core 20 from aproximal end 12 a to a distal end 12 b of the shank 12. The thread 14includes proximal and distal facing flanks 14 a, 14 b that extendbetween a root 14 c and a substantially flattened crest 14 d. The thread14 defines a major diameter d₂ of the shank 12, which can vary along thelength of the shank 12, but the major diameter d₂ is preferablysubstantially constant along a substantial portion of the shank 12. Thethreads 14, however, can taper at the distal portion of the shank 12 toterminate at an apex 22 which forms the distal tip of the shank 12. Thecore 20 of the shank 12 defines a minor diameter d₁ that can also besubstantially constant or can vary along the length of the shank 12. Asshown in FIG. 1A, the core 20 tapers from a proximal end 12 a to adistal end 12 b. A person skilled in the art will appreciate that theshank 12 shown in FIG. 1A is merely an exemplary embodiment of a shank12, and that a variety of different shanks having differentbone-engaging features can be used with a suture anchor 10 in accordancewith the present invention.

[0024] The head 16 of the suture anchor 10 is shown in more detail inFIGS. 1C and 1D, and is attached to, or more preferably is formedintegrally with, the shank 12. The head 16 has a generally oval shapedefining a minor diameter x₁ and a major diameter x₂. In an exemplaryembodiment, the minor diameter x₁ of the head 16 is about three-fourths(¾) the size of the major diameter x₂ of the head, and the majordiameter x₂ of the head 16 is equal to or less than the minor diameterd₁ of the shank 12. The relatively small size of the major diameter x₂of the head 16 as compared to the minor diameter d₁ of the shank 12 isparticularly desirable so that the head 16 will not require a largerbone tunnel to be formed in the bone than is necessary. The head 16further includes a length Lh (shown in FIG. 1B) that extends between theproximal and distal ends 16 a, 16 b thereof. The length L_(h) of thehead 16 can vary, but preferably the length L_(h) of the head 16 isoptimized to allow the head to be received within a driver tool and tobe driven into bone without shearing off.

[0025] The head 16 of the suture anchor 10 further includes at least onesuture attachment member formed thereon or therein for receiving one ormore sutures. While a variety of suture attachment members can be used,FIGS. 1A-1D illustrate an exemplary embodiment of the suture anchor 10having first and second suture tunnels 26 (only one tunnel 26 is shown)that extend through the head and that allow a length of suture to bedisposed therethrough. The first and second suture tunnels can extend atvirtually any orientation through the anchor head, but they preferablyextend transversely through the anchor head 16 at different positionsalong the longitudinal axis A of the anchor 10 to prevent the tunnelsfrom intersecting, so as to preserve the structural integrity of thehead 16. In an exemplary embodiment, the suture tunnels terminate at aposition proximal to the distal end 16 b of the drive head 16 to providea channel-free portion 24 (shown in FIG. 1B) in the head 16. Since thedistal portion of the anchor head 16 is typically the part of the anchor10 that is under the most stress during insertion, the channel-freeportion 24 provides a much stronger, more dense portion of the anchorhead 16 that will minimize the risk of shearing during insertion.

[0026] The suture anchor 10 can also optionally include fourlongitudinally oriented suture-receiving grooves or channels 18 a, 18 b,18 c, 18 d formed therein. The suture-receiving channels 18a, 18 b, 18c, 18 d are formed in the outer surface of the head 16 and arepreferably spaced equidistant from one another. As shown in FIG. 1D, twoopposed suture-receiving channels 18 d, 18 b are positioned along themajor diameter x₂ of the anchor head 16, and the other two opposedsuture-receiving channels 18 a, 18c are positioned along the minordiameter x₂ of the head 16. The position of the suture-receivingchannels 18 a, 18 b, 18 c, 18 d can also vary, but preferably theyextend through the proximal surface 16 c of the drive head 16 andterminate at an opening of the corresponding suture tunnel. Where thesuture tunnels are positioned proximal to the distal end 16 b of thedrive head 16, the suture-receiving channels 18 a, 18 b, 18 c, 18 dpreferably also terminate at a position proximal to the distal end 16 bof the drive head 16 to provide a channel-free portion 24 (shown in FIG.1B) in the head 16. Moreover, where two suture tunnels are provided atdifferent locations along the length of the drive head 16, a first pairof opposed suture-receiving channels, e.g., suture-receiving channels 18a, 18 b, can have a length L₁ that is different than a length L₂ of asecond pair of opposed suture-receiving channels, e.g., suture-receivingchannels 18 c, 18 d, as shown in FIG. 1C.

[0027] The size and depth of each suture-receiving channel 18 a, 18 b,18 c, 18 d can also vary, but they should be effective to seat a sutureflush or sub-flush with the head 16 to allow the head 16 to be engagedby a driver tool without interference by the suture. In an exemplaryembodiment, about 20% to 30%, and more preferably about 28%, of across-sectional surface area of the drive-head 16 is removed to form thesuture-receiving channels 18 a, 18 b, 18 c, 18 d. As a result, the drivehead 16, having suture-receiving channels 18 a, 18 b, 18 c, 18 d formedtherein, will have a cross-sectional surface area at the proximal-mostsurface that represents about 72% of a nominal cross-sectional surfacearea within a perimeter of the drive head 16.

[0028] A person skilled in the art will appreciate that a variety oftechniques can be used to attach a suture to an anchor, and that theanchor 10 is not limited to having one or more suture receiving tunnelsand/or one or more suture-receiving channels.

[0029] In use, the suture anchor 10 can be driven into bone using adriver tool, such as tool 50 shown in FIG. 2A. The driver tool 50 canhave a variety of shapes and sizes, but preferably includes an elongateshaft 52 having a proximal, handle portion 54 and a distal end 56 havinga socket 58 (FIG. 2B) formed therein and adapted to seat the head 16 ofthe suture anchor 10. The socket 58 of the driver tool 50, which isshown in FIG. 2B, has a substantially oval shape to fit around theoval-shaped head 16 of the anchor 10. The size of the socket 58 shouldbe sufficient to provide a secure fit between the oval-shaped head 16 ofthe anchor 10 and the tool 50, and to prevent rotation of the tool 50with respect to the anchor 10. The driver tool 50 also preferablyincludes an inner lumen (not shown) extending therethrough for receivingthe remaining free ends of the suture(s) threaded through the head 16 ofthe anchor 10.

[0030] The suture anchor 10 can be used for a variety of medicalprocedures. In an exemplary embodiment, the suture anchor 10 is used incontext of an arthroscopic shoulder repair, and more specifically, forattaching a detached labrum (as might result from a Bankart lesion orrotator cuff tear) to the glenoid rim of a scapula. It will beunderstood, however, that the system and method described herein areequally applicable to connecting detached tissue in other contexts aswell. Further, the method described is merely exemplary of the stepsinvolved in using any of the embodiments of the anchors of the presentinvention.

[0031] The procedure generally requires a delivery guide, e.g., a hollowguide tube, to be positioned at a desired implant site in the vicinityof a joint. A tap, or more preferably, an awl or a punch is theninserted through the tube and rotated until the depth mark reaches thecortical surface of the patient's bone. A length of suture is thenthreaded through each tunnel (only tunnel 26 is shown) in the head 16 ofthe anchor 10, and the remaining portion of the sutures are passedthrough the lumen in the driver tool. The free ends of the suturesextending out of the proximal end 54 of the driver tool 50 canoptionally be pulled to hold the suture anchor 10 in the socket 58 ofthe driver tool 50. The anchor 10 can be then be inserted into bone byremoving the tap from the delivery guide and introducing the drive toolwith the anchor attached thereto through the delivery guide. The drivertool 50 is then twisted clockwise, applying a slight forward pressure,until the anchor 10 is at the desired depth. The driver tool 50 can thenbe removed by pulling straight back, which will expose the suture anchorand the sutures extending therefrom. The surgeon can then approximatethe free end of detached labrum to the surface of the bone adjacent tothe suture anchor, and the sutures can then be threaded through detachedlabrum and tied to secure the detached labrum to the bone.

[0032]FIGS. 3A and 3B illustrate the advantages of a suture anchor 10according to the present invention compared to conventional, prior artsuture anchor drive heads, such as the hexagonal-shaped head 70 and thesquare-shaped head 80 shown. Each anchor head 16, 70, 80 shown has asize that is adapted to fit within a driver tool having a socket havingthe same shape as the shape of the corresponding anchor head of theanchor to be driven into bone by the driver tool. The outside diameterof each corresponding driver tool however, is the same for all threeanchor heads 16, 70, 80. During insertion of the anchor into bone, atorque is created by the driver tool 50. At some point, the torquecreated by the driver tool can cause the anchor head to strip, whereinportions of the outer surface of the head are removed thus allowing thehead to rotate within the driver tool. FIG. 3B illustrates the portions72, 42, 82 that would need to be removed in order for each of theillustrated anchor heads 70, 16, 80 to be stripped, e.g., to allowrotation of the anchor head within the socket in the driver tool. Thisis further indicative of the amount of material on the anchor head thatinterfaces with the driver. As shown, the portion 72 of thehexagonal-shaped anchor head that needs to be removed is less than theportion 42 of the anchor head 16 of the present invention that needs tobe removed in order for the anchors to be stripped. The portion 82 ofthe square-shaped anchor head 80 that needs to be removed is moresimilar to the portion 42 on anchor head 16 that needs to be removed toresult in stripping. However, the total cross-sectional area of the ovalanchor head 16 is larger than the total cross-sectional area for thesquare head 80. As a result, the amount of material that interfaces withthe driver on the oval head 16 is much larger than that for the squarehead 80. Thus, overall, the oval head has an increased strippingstrength compared to the prior art anchor heads 70, 80.

[0033] The following table, which is based on each of the anchor heads16, 70, 80 having dimensions such that each anchor head 16, 70, 80 isadapted to fit within a driver tool having the same outer diameter,further illustrates the differences between the prior art anchor heads70, 80, and the anchor head 16 of the present invention: TABLE 1 PERCENTOF MATERIAL THAT TOTAL CROSS- AREA OF MATERIAL THAT NEEDS TO BESECTIONAL SURFACE NEEDS TO BE REMOVED TO REMOVED TO RESULT Anchor HeadAREA RESULT INSTRIPPING IN STRIPPING Hexagonal Anchor Head 70 0.0089 in²0.00073 in²  8.2% Oval Anchor Head 16 0.0105 in² 0.00240 in² 22.8%Square Anchor Head 80 0.0060 in² 0.00200 in² 33.3%

[0034] As shown in Table 1, since the anchor head 16 of the presentinvention requires more material to be removed to result in stripping ofthe head than the hexagonal anchor head 70, and since the anchor head 16of the present invention has a much larger cross-sectional surface areacompared to the square anchor head 80, the suture anchor 10 of thepresent invention will have a much higher stripping strength than theprior art anchors. In other words, the anchor head 16 of the presentinvention has a higher driver-to-anchor interface than the prior artanchors.

[0035]FIGS. 4 and 5 illustrate further advantages of the anchor 10 ofthe present invention over prior art anchors. The prior art anchorstested include the Prior Art 1: 5 mm Hex, the Prior Art 1: 6.5 mm Hex,and the Prior Art 2: 6.5 mm Hex. The Prior Art 1 anchor has a loopmolded into and embedded within the anchor head to receive a length ofsuture, and the Prior Art 2 anchor has transverse suture-receiving boresformed therein. The suture anchors of the present invention are referredto as the Present Invention: 5 mm Oval, and the Present Invention: 6.5mm Oval. As shown in FIGS. 4 and 5, the anchors of the present inventionhave a pullout tensile, tested using 25D foam, and a failure torque thatis greater than the pullout tensile and failure torque of the prior artanchors. Accordingly, the suture anchor 10 of the present inventionshows a significant improvement over prior art anchors.

[0036] The suture anchor 10 of the present invention can be formed froma variety of materials, and can be formed from separate parts which aremated to one another. Preferably, however, the suture anchor 10 isformed as a single unit from a material that is suitable for humanimplantation, such as metal or plastic, and that is somewhat resilient.Exemplary materials include, for example, metals, metal alloys,absorbable polymers, such as, but not limited to, polylactic acid,polyglycolic acid, and copolymers thereof, non-absorbable polymers, suchas, but not limited to, polyethylene, polypropylene, polyurethane, andacetal, and bioceramic materials, such as blends of polymers containingtricalcium phosphate, calcium sulfate, calcium carbonates, and hydroxyappatite.

[0037] One skilled in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

What is claimed is:
 1. A suture anchor, comprising: an elongate shankdefining a longitudinal axis and having at least one bone-engagingthread formed thereon; and a drive head having a proximal end and adistal end mated to the elongate shank, the drive head having asubstantially oval shape and at least one suture attachment memberformed in a portion of the drive head.
 2. The suture anchor of claim 1,wherein the suture attachment member comprises at least one suturetunnel extending transversely through the drive head.
 3. The sutureanchor of claim 2, further comprising a longitudinally orientedsuture-receiving channel formed in an outer surface of the drive headand originating at and extending proximally from each opening of the atleast one suture tunnel.
 4. The suture anchor of claim 3, wherein the atleast one suture tunnel is formed proximal to the distal end of thedrive head to form a channel-free portion in the drive head.
 5. Thesuture anchor of claim 3, wherein the suture-receiving channels areadapted to seat a suture flush or sub-flush with the outer surface ofthe drive head.
 6. The suture anchor of claim 1, wherein the sutureattachment member comprises a first, transversely oriented suture tunnelextending between a first pair of opposed, longitudinally orientedsuture-receiving channels formed in an outer surface of the drive head,and a second transversely oriented suture tunnel extending between asecond pair of opposed, longitudinally oriented suture-receivingchannels formed in an outer surface of the drive head.
 7. The sutureanchor of claim 6, wherein the suture-receiving channels are adapted toseat a suture flush or sub-flush with the outer surface of the drivehead.
 8. The suture anchor of claim 6, wherein the drive head has across-sectional surface area at the proximal-most surface thatrepresents about 72% of a nominal cross-sectional surface area within aperimeter of the drive head.
 9. The suture anchor of claim 1, whereinthe drive head has a failure torque of at least about 5.0 inch pounds.10. The suture anchor of claim 1, wherein the at least one bone-engagingthread comprises a helical thread.
 11. The suture anchor of claim 1,wherein the elongate shank tapers from a proximal end to a distal end.12. A suture anchor and installation kit, comprising: at least onesuture anchor having a longitudinal axis and a shank with bone-engagingthreads formed thereon, and a drive head having an oval shape formed onthe shank, the drive head having at least one suture tunnel extendingthrough the drive head such that the suture tunnel intersects thelongitudinally axis; and a cylindrical driver tool having a distal endwith a socket formed therein having an oval shape adapted to receive andengage the drive head of the suture anchor.
 13. The kit of claim 12,wherein the driver tool has an outer diameter that is equal to or lessthan an outer-most diameter of the suture anchor.
 14. The kit of claim12, further comprising a longitudinally oriented suture-receivingchannel formed in an outer surface of the drive head and extending froman opening of each of the at least one suture tunnels.
 15. The kit ofclaim 14, wherein each suture-receiving channel extends through aproximal-most surface of the drive head and terminates at the opening tothe suture tunnel.
 16. The kit of claim 15, wherein the at least onesuture tunnel extends through the driver head at a position proximal toa distal end of the drive head to form a channel-free portion in thedrive head.
 17. The kit of claim 14, wherein the drive head includesfour longitudinally oriented suture-receiving channels formed therein.18. The kit of claim 17, wherein the drive head has a cross-sectionalsurface area at a proximal-most surface that represents about 72% of anominal cross-sectional surface area within a perimeter of the drivehead.
 19. The kit of claim 12, wherein the drive head has a failuretorque of at least about 5.0 inch pounds.
 20. The kit of claim 12,wherein the at least one bone-engaging thread comprises a helicalthread.
 21. The kit of claim 12, wherein the shank of the suture anchortapers from a proximal end to a distal end.
 22. A method for attachingtissue to bone, comprising the steps of: forming a bone cavity within abony structure; providing suture anchor having a shank withbone-engaging threads formed thereon, and a drive head having an ovalshape formed on the shank, the drive head having at least one suturetunnel extending through the drive head, the suture anchor furtherincluding at least one length of suture head extending through the atleast one suture tunnel and having free ends extending therefrom;attaching an inserter tool to the suture anchor; inserting the sutureanchor into the bone tunnel such that free ends of the at least onelength of suture extend from the bone tunnel; removing the insertertool; and attaching the at least one length of suture to tissue toproximate and attach the tissue to the bony structure.